BEFORE I SAW it myself, a reader alerted me that she’d come upon a new book I shouldn’t miss, called “Innumerable Insects.”
“I’m just a nurse interested in the world, not a biologist,” said Teresa in her kind note to me. “And yet,” she said, “I found it very compelling and full of ancient, beautiful illustrations.”
Dr. Michael Engel is the author of “Innumerable Insects: The Story of the Most Diverse and Myriad Animals on Earth,” lavishly illustrated with historic prints from the American Museum of Natural History Library collection. Dr. Engel is a research affiliate at the museum, and also University Distinguished Professor of Ecology and Evolutionary Biology and Senior Curator of Entomology at the University of Kansas.
We talked about the most primitive of insects–the wingless but wonderful bristletails (my favorite); about how insects hear; about insect evolution; about how bees are just a subset of wasps who decided to be vegetarians, and more.
Read along as you listen to the Nov. 12, 2018 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).
Plus: I’ll give away a copy of the book; enter to win in the comments box at the very bottom of the page.
‘innumerable insects,’ with dr. michael engel
Q. I’m grateful to Teresa, my reader, who I don’t know, for sending me that note to turn me on to the book, so I found it right away. I believe you coauthored an entire 772-page textbook on insect evolution, or something around that scale. And now, lucky for sort of us laypeople, you’ve created this book, which traces their history, among other things. Tell me a little bit about the project. How did it happen?
A. Well, the American Museum of Natural History has, for several years now, attempted to bring forth to the public the rich trove of treasures that are sitting in their rare book collection, books that are not generally accessible to the public.
And so, I can’t remember now, but several years back, they sort of did an introductory volume just titled, “The Natural Histories,” where they featured a few examples of a variety of things, from marine organisms to birds, even a few insects, where they just showed some of the more stunning images from the rare book collection, and then had little vignettes of text about the author of that particular book, and maybe a few details on the illustrator who produced the images.
And then from there, they kind of then did a series of books where they focused more in on very specific topics, again, highlighting the rare book collection. And so they did a volume, “Extraordinary Birds,” “Opulent Oceans,” and about two years ago, they approached me with the suggestion that maybe it was time to do one focused on insects.
Q. Innumerable insects, specifically. [Laughter.]
A. Yes. Insects comprise a vast majority of life on earth, and they have, perhaps, one of the best rare book collections for insects in the world. It was just sort of a natural opportunity to kind of tell the tale of insect evolution, and also feature these amazing works from which our many entomological discoveries were first illuminated.
Q. So the subtitle says, “The Most Diverse and Myriad Animals on Earth.” So just how many are we talking about?
A. Well, to date we’ve described, in total of all life, from bacteria to large vertebrates like deer and monkeys, we’ve described about 2 million species on earth, and 1.1 million of those are insects.
Q. Oh, my.
A. So more than half of all life that has been documented on this planet falls among the insects, and where a new bird or a new mammal is rightly heralded in the press at any given time, what kind of silently goes on in the background is that each year, thousands upon thousands of new insect species are being added and discovered. And so the rate at which we continue to discover new insect species just is growing.
Q. And many of those that sort of either once crawled or flew around the earth, they’re already gone, right? I mean, the 1.1 million, you’re talking extant or the ones we’ve described? I wasn’t sure.
A. The 1.1 is the living diversity around us. So it does become all the more mind-blowing when you think that 95 percent of all life that has ever lived in the last 4 billion years is, 95 percent of that diversity is already gone. And yet we still have 1.1 million insects, and growing.
Q. It is. It’s staggering, isn’t it?
One chapter is called, “The Earliest of the Six-Legged.” I love that chapter title. But what does an animal have to do—and also I love, by the way, laypeople like myself are often afraid to say animal when we talk about insects, as if we should distinguish between the two. And so I love the fact that in this book, they’re animals, do you know what I mean? I know it may sound silly to you. But it’s as if, generically speaking, laypeople often distinguish, and it’s not necessary.
But what does an animal have to do, besides have six legs, to be an insect?
A. Well, that’s a good question. As a matter of fact, it’s clearly not just six legs, because there are other arthropods that have six legs that are not insects. So insects belong to this larger group called the Hexapoda, which is aptly named, meaning six feet. So the hexapods all have six legs, and they include some rather unfamiliar little things like springtails and so forth, and then the true insects. So what is it that makes, if it’s not just the six legs, what is it that makes an insect an insect?
One of the most defining features of an insect is not something that you’re going to immediately notice upon looking upon them, and that is, inside of the antenna, you know, the antenna has many little segments that it’s composed of. And the second one of those segments has a special name, it’s called the pedicel. And within the pedicel is this, it’s called a chordotonal organ, and it’s a highly sensitive organ that basically, to oversimplify it, picks up on very subtle vibrations.
And it can be highly attuned, so that insects can really get an amazing perception of their world through this very specialized organ. So much so that, for example, among some of the flies, it is so finely tuned and has so many nerve endings within it, they can pick up the vibration of another fly, and they’re able to tell whether that fly is of the same species, or even if that’s a male or a female of the same species.
A. And whether it’s a potential mate. All from the very fine vibrations it’s detecting with this very highly specialized organ in the antenna. So it really expands the sensory world of these six-legged organisms, and that is one of the most defining features of an insect, even though it’s not something you’re immediately going to look down and be like, “Wow, look at that”-
Q. Pedicel. [Laughter.]
A. … chordotonal organ.” There are also some other features. So insects have a very specialized structure at the back end of their body that the other six-legged animals do not have. It’s called an ovipositor, and it’s used, as its name suggests, to place eggs. And so it’s basically an egg-laying structure that allows insects to very precisely position eggs, most importantly, among some of the more primitive insects, in little crevices and various safe spots so that they’re not just too easily accessible by potential predators, or to desiccation, or various other factors that would reduce their fecundity.
Q. So we would have this special organ to feel the vibrations, and we have an ovipositor. We have six legs, so those are some of the sort of qualifications for being an insect?
Q. Yes. Now, I’m going to oversimplify, but insects descend from crustaceans. They came out of the sea, and onto the land, and eventually they learned to fly. Did they sort of invent flight? Is that the trajectory of their evolution, roughly? [Laughter.]
A. Yes. In a nutshell, yes. Insects were the first to fly. They did so about 170 million years before anything else joined them in the air. And the ones that eventually first, the next comers-along, if you will, were the pterosaurs, and they were then followed by birds, and eventually later on by bats.
But so for a vast period of time, a period of time twice that since the extinction of dinosaurs, insects were the sole thing in Earth’s skies. And they were up there, floating about, with all their aerial acrobatics, long before any vertebrate ever came along to mimic them.
And so I think that tends to get forgotten and overlooked that when one sees sort of like a bumblebee humming before a flower, or a butterfly flitting through your garden, you’re looking at the summation of more than 400 million years of evolutionary refinement, in terms of insect flight.
Q. It’s pretty astonishing, isn’t it? And that was one of the things that in reading the book, I came away with. It was very clear. And I think the historic plates that were utilized and the text really brought that to life for me.
Now when I asked you what I needed, if I were an animal, to be an insect, you didn’t mention wings because wings—the first insects didn’t necessarily have them. And I’ve confessed to you in email that I have an obsession with one of those very primitive insects, a wingless creature that I know as a bristletail [above].
And I love moths, and I go out in the dark a lot looking for moths, and photographing moths, and I’ve done this for a number of years. And when you do that, you meet creatures you don’t see during the day. [Laughter.]
And so the bristletails were a creature that I met a number of years ago in my garden, and I looked them up and I found out what they were. And I found out in reading about them things like, they were from maybe the Devonian period, and that they have “elaborate courtship rituals,” and that they take two years to come to sexual maturity. All these things that seemed impossible for such a tiny thing. How could it even live two minutes, let alone two years or longer, and have elaborate anything?
Do you know what I mean? It was so … it just opened the world to me. So can you tell me a little bit about those types of primitive wingless creatures that are insects?
A. Yes. The most primitive of all insects are as you mentioned the bristletails, and they’re among, they have another primitive group called the silverfish, sometimes also known as firebrats. People may know them by that name. And they were groups of insects, they represent sort of this primitive group of insects before flight came about. And so by the time flying insects first appeared, bristletails and silverfish were already on the scene, and they would have been looking at the flighted insects as sort of young newcomers. They were already ancient by that time.
And yes, we have evidence of them going back to the Devonian, which is approaching 400 million years ago. But based upon other evidence from the fossil record of all insects, there’s a great indication that they probably go back even further, maybe even into the latest part of the Silurian, although there are very few deposits from which we can extract information, at least at the current time. But in time, I’m pretty certain that we’ll find that they go back even further.
Bristletails and silverfish are fascinating little animals.
Q. Yes, they are.
A. You see there the kind of these holdouts, these relics of a much more ancient age. But that doesn’t mean that they just don’t do much. In their own way, they’re very specialized. Just because something is ancient doesn’t mean it’s just primitive in all respects. They’ve been around for a long time, but during that time they’ve evolved their own specializations, and some of those you mentioned. Their courtship rituals are quite fascinating.
Q. Yes. It’s amazing when you, if you take the time to find out—if you see something like that, and it’s a little speck. It’s, you think, nothing, but it’s something; it’s this enormous, as you say, 400 million years of history, and this complexity and this survival against all odds through all of that. And I mean, I just find it chilling, fascinating and chilling.
So what I loved in the book is I guess it’s a little bit chronological, that you talk about here was something like a bristletail or a silverfish, and there were no wings, and eventually some of the first wings came. And the designs of those wings weren’t necessarily the kind that can fold flat against your back like some insects we may be more familiar with. And that, for instance, dragonflies are not as primitive, but they have earlier wing designs, yes?
A. Yes. Dragonflies, among our living diversity, dragonflies and a group called mayflies have what you might call the most primitive of wing design. Now that is not to say that they’re the most primitive of winged insects. There are various extinct lineages that were ancient long before a dragonfly ever flew over this world, or long before a true mayfly appeared. None of those groups have common names that I can refer to, because they never survived to the present day to get common names.
A. So in that regard, dragonflies and mayflies are newcomers, but relative to the other flying insects that we have today, they do represent a fragment of this much more ancient diversity. And as you mentioned, very rightly, one of the aspects of the primitive nature of their wings is the inability to fold the wings.
And so, and that’s not to say that they can’t fold them in terms of moving them up and down in flight. Obviously, they’re doing that. But in terms of when not in use, being able to kind of collapse them back over the back of the abdomen. So as one thinks of seeing, say, a wasp or a bee land on a plant, and they’re no longer in flight, the wings kind of collapse backwards and fold nicely back over the abdomen, or as in a cricket or a grasshopper, the same sort of phenomenon is going on.
Instead, if you think of an image of a dragonfly sitting on a reed, their spectacular wings are stuck straight out from the body, or a damselfly, where they’re sticking straight up into the air. And it’s because they lack that specialization in order to collapse the wing back over the abdomen and get it out of the way when not in use.
Q. It was, there was sort of the word of the day, there, I think, in that section, and I’m not sure how to pronounce it, as paleopterous?
A. Yes. Paleopterous.
Q. Paleopterous. And that means?
A. Primitively winged.
Q. There were a lot of great words in the book. You scientists have so many, you have a language of your own, don’t you? [Laughter.] You have a word for everything.
Q. Almost. So some insects seem to sing. To us, we hear them at night in the summer, for instance, crickets, katydids, grasshoppers. Do they have ears if they’re singing? Do they hear each other? Do they have ears? What about the range of hearing devices and capabilities in insects?
A. Indeed they do. There would be little point to making a sound if there was no one to hear it, aside from us. [Laughter.] They’re usually not singing to us, so. Yes, they actually have quite a spectacular range of hearing devices, and they’re not like what we would typically think of. They are somewhat similar in the sense that, like an eardrum, it does usually consist of some sort of tympanum, sort of a thin area of membrane with a cavity behind it and some nerve endings. And so the vibration hits sort of the drum, if you will, and transfers that information to the nerve endings, and it says, “O.K., you’ve just detected this particular sound.”
But in terms of the placement of these hearing devices, they’re in places that we would think that are quite bizarre. We’re so very used to our mammalian view of the world that ears have to be on either side of the head, whereas they’re not in insects. So in some of the more famous examples that you mentioned, like crickets, katydids, and grasshoppers, in many cases they may even be located on the legs, so you can think of it being like an ear on your knee.
Q. Interesting. [Laughter.]
A. Using this in order to hear the calls, but perhaps an even more bizarre example is the cyclopic ear of some praying mantises, where they have a single ear rather than, you know, we have two ears and even the crickets and katydids and everything, where they have them on their legs, they still have two, one on each leg. Or they, if they have them on the abdomen, they have one on the right side and one of the left side. But then there are some that they don’t have two at all. They just have one great one that’s sitting in the center of their chest.
And so there’s all sorts of interesting modes of listening going on among insects.
Q. There was one fun kind of statement [in the book] when you were talking about the relatives ants, bees, and wasps. You said, “Ants and bees are really modified wasps.” Can you explain that a little bit?
A. Yes. So and along with that, at the same time, butterflies are merely nothing more than modified moths.
A. It’s this sort of phenomenon, and what it is, is first you evolved this diversity of wasps in this order called Hymenoptera, which includes ants, bees, and wasps. And then from among this diversity of wasps, there was a subset of those wasps that shifted to a strictly vegetarian diet, collecting pollen and bringing that pollen and nectar back to the nest and feeding it to their young. And we give them a specialized name as bees, but really they are nothing more than this one group of wasps that took on a very modified diet.
A. And the same sort of thing is with ants. Ants are just a lineage derived from within this great diversification of wasps, and they live in these very complex, large, perennial societies. They have a worker caste that has given up its wings and lost the ability to fly and lost the ability to reproduce, the sterile worker caste. And then they’re ruled over by the queen ant, and so forth and so on with this defined caste system, much as in honeybees. And we give them their own specialized name as ants, because they look so much different than the rest of the wasps from which they derived.
Q. Interesting. I wanted to ask you something not about the book “Innumerable Insects,” but I love to share photos of creatures I see outside, whether at night or in the daytime, and I’m always looking them up and putting sometimes, if I can’t ID them myself on bugguide.net, and maybe participating in citizen science projects and so forth.
And I was wondering as an entomologist, has the sort of advent of more of that with technology, along with technology, the ability for people to share more data, more photographs and so forth, and sightings—has that come into play in helping you with research in any way?
A. Sometimes. It helps some of my colleagues more so than myself, but it’s definitely a wonderful advent of our current age. People are able to go out, take images, and help in some cases. Basically, having more eyes on the ground is always a good thing, and people are able to help document expanding or contracting distributions of species, very odd records, odd occurrences, new occurrences, new behaviors, new ecologies that are being observed by everyone who is out looking.
There’s a little bit of a double-edged sword, though, at times, because sometimes people are eager to, obviously, get the species that they’ve photographed identified authoritatively.
Q. Right. [Laughter.]
A. And whereas in some cases, that’s easy to do. We’re very happy to do it. Sometimes people get a little bit frustrated when the answer is, “Well, it could be species X or species Y,” but in that particular group there are a whole slew of species that look virtually identical, superficially similar, and that the only way to really tell the difference is through such minute details that can never be captured even in a stunning of image, and stunning photograph. And so they have a gorgeous, beautiful image, and there’s no doubt it’s a fabulous image, but without the actual organism in hand, you’re left kind of with the, “Well, if this, then that, maybe,” you know.
A. And sometimes people get a little bit frustrated that it’s not quite so simple to just give a black and white answer. And there is then, a little bit of danger for someone who does want to just quickly snap off an answer and be like, “Oh, yes, that’s definitely species Y,” without being a bit more hesitant to be like, “Well, the reality is, we really should look into it a little bit further.”
So anything, it’s a lot of good and a little bit of bad. [Laughter.]
Q. Yes. Well, Michael Engel, I’m so glad that you could take the time to talk about “Innumerable Insects,” and also just for the work you did to create this wonderful book, so thank you so much.
enter to win ‘innumerable insects’
I’LL BUY A COPY of “Innumerable Insects” by Dr. Michael Engel for one lucky reader. All you have to do to enter is answer this question in the comments box at the very bottom of the page:
What insect(s) are you fascinated by (the way I am mad for those ancient bristletails)? Tell us why.
No answer or feeling shy? Just say something like “count me in,” and I will. But an answer is even better. I’ll draw a random winner (US and Canada only) after entries close at midnight Tuesday, Nov. 20, 2018. Good luck to all.
(Color plates from the collection of the American Museum of Natural History Library, and used in “Innumerable Insects.” Used by permission.)
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